Electrostatic facsimile receiver



Aug. 23, 1955 c. J. YOUNG 2,716,048

ELECTROSTATIC FACSIMILE RECEIVER Filed Aug. 14, 1952 4Z 2727-5 BY fl TTOR NE Y United States Patent O ELECTROSTATIC FACSIMILE RECEIVER Charies 3. Young, Princeton, N. J., assigner, byy mesne assignments, to United States of America as represented by the Secretary of the Army Application August 14, 19521, serial No. 304,263 y 1 claim (el. 346-74) is employed directly in producing the record, without the l intervention of any optical or photographic apparatus.

It has been proposed Vtoproduce records in vfacsimile systems using a cathode ray tube scanning means by first charging uniformly a selenium plate which is then exposed to light resulting from the cathode raybeam action upon the phosphor screen of the cathode ray tube, thus selectively discharging portions of the selenium (plate. According to this mode of operation, a dusting powder of known composition which is charged with a voltage of a given polarity is spread upon the selectively discharged plate, The powder adheres to those portions of the plate having a polarity opposite to the polarity of the plate, in a manner well known in the art. rThe selectively coated plate is then placed against a sheet of paper or similar material for the purpose of transferring the powder image to the paper where it is xed by heating orjother means.

The above-described mode of producing facsimile records is objectionable in that the selenium plates are diiiicult to produce and the operation is, therefore, rather expensive; additionally, the method requires a separate step of contacting the plate with the transfer paper which, of course, adds appreciably to the time required for conducting the operation. v

In another known system for producing facsimile records, the light emanating from the phosphor screen of the cathode ray tube in the receiver is caused to scan a sheet of material which is provided with a photosensitive layer. The photosensitive layer, which may be in the form of a conventional silver halide lmis then processed in accordance with conventional photographic methods for developing and xing the image of the scanning light. This method is subject to the same criticism of expensiveness because of the high cost of the photosensitive paper.

It is, therefore, a primary object of the invention to provide a system for making permanent records of a facsimile image, which system does not require the use of a costly selenium plate or photosensitive film.

A further aim of the present invention is that of providing means for recording in permanent form the image of a cathode ray scanning vbeam on paper or similar inexpensive material. v

Still another object of the invention is that of providing means for employing the cathode ray beam of a CR tube, in the making of facsimile records, which means does not require the use of flight links or other optical systems. y

HIn general the inventioncontemplates ,the scanning of a cathode ray beam directly onto a paper record. member whichvmay either be uniformly charged, to begin with, or without any electrostatic charge, the electron beams being caused to travel through a Lenard window in the face of the tube to charge or discharge the paper selectively,

2,715,048 Patented Aug'.` 23, 1955 depending upon whether the paper record vmember employed is used without a prior electrostatic charging or with a uniform charge. As will appear from the detailed description of the drawings, the present system requires no photographic material or other expensive aids and is accomplished in a minimum amount of time.

Since the beam of electrons which emerges from the Lenardwindow will ionize any air molecules present in front of such window it hasy been found desirable to avoid the production of ions, since such ionization tends to reduce the definition of the image produced on the paper record strip.

vIt is, therefore, still another object of the present invention to bombard a record strip with a cathode ray beam in a space which is substantially evacuated.

Still another object of the invention is to provide means for passing the record receiving strip as close to the Lenard window as is practicable, thus decreasing the distance which the electron beam must travel from the 'ice window to the record strip.

The inventionhas as a further aim that of providing means whereby the record strip may be used without the necessity of employing anyevacuating means, namely,

Figure-3 is an enlarged fragmentary View of a portiony of the apparatus of Figure 1; f i .j

Figure 4 is an enlarged fragmentary view of a modie'd form of apparatus corresponding to Figure 3;

Figure 5 is a vertical sectional `fragmentaryview of still-another modication and; ,i

Figure 6 is a fragmentarylplanview of -the device shown in Figure 5. l i

f Referring more particularly to the drawings, Figure 1 illustrates a system for producing a permanent record of a facsimile image, including a special type of cathode ray tube10 having a Lenard window 11. A strip of record paper 12 is supplied from a supply roll 13 from which the paper is drawn over an idler roll 14 between a pair of charging electrodes 15 and 16 and thence before the Lenard window, over a second idler roll 17 which is mountedfor rotation about an axis'l'parallelv to the Lenard window, as. will be more speciiically explained hereinafter.- From the idler roll 17,- the paper travels pasta heater 19 to a driving roll arrangement 20, 2l, thelatter roll being driven by'a suitable device such as an electric motor 22 energized from a suitable source of electricity illustrated in the drawings as being a conventional 60 cycle, 110 volt source. i,

Disposed over the path of travel of ythepaper strip from idler roll 17 to driving rolls 21 is a dispensing receptacle 23 adapted to be filled with glass beads and finely divided powdered material 24 which are permitted to drop onto the surface of the paper strip 12 and to cascade from such strip into a second receptacle 25. The particulate material which drops off the paper strip into the receptacle 25 may be returned to receptacle 23 for reuse by suitable means such as a feed screw, shown schematically by the dashedl line 26. .j

The cathode ray tube designated generally by reference numeral 10 comprises an envelope 27 in which are located the known elements of a cathode rayv tube, including a cathode 28, control electrode 29 and horizontal deflecting plates 30. The cathode is illustrated as being heated by means energized from a suitable source of 60 cycle, 110 voltage. In a manner well known in the high speed electronic facsimile art, an image signal together with horizontal sync pulses is received by the facsimile receiver 31. In the receiver 31 are circuits for separating the input image signal from the horizontal syne pulses and impressing the image signal upon the input terminals of an amplifying means indicated generally at 32, while the horizontal sync pulses pass to the horizontal sweep circuit means 33. The input image signal, after having been amplified at 32 is impressed upon the control electrode 29 of the cathode ray tube, while the horizontal sweep voltage is supplied to the deflecting plates 30, in a manner well known to those skilled in the art.

Vertical deflection plates 30a are also provided in the cathode ray tube in the conventional way. These are not essential to the basic operation of the invention but are of assistance in bringing the path of the horizontally deflected beam into register with the narrow slit 11.

Instead of having a conventional phosphor-coated glass end, the cathode ray tube employed in practicing the present invention is provided with a generally rectangular metal cap member 34 which is provided with the opening 11 mentioned above. As shown more clearly in the enlarged fragmentary view of Figure 3, the opening or window 11 in theend of cap member 34 is covered by an extremely thin sheet of metallic foil 35, e. g. aluminum foil, which may be approximately 0.0003 inch in thickness.

The Lenard window 11 may be in the form of a slit approximately 8 inches in length and only 0.008 inch in width. As is known, the aluminum or other foil 35 which is employed to cover the Lenard window slit 11, is by virtue of its extreme thinness, reasonably transparent or permeable insofar as an electron beam at high voltage is concerned. The interior of the cathode ray tube 10 is maintained free of air or other gas, and the maintenance of such vacuum is further insured by the provision of a gasket-like sealing means 36 disposed between the cathode ray tube envelope 27 and the rectangular cap member 34.

Maintenance of the vacuum in the tube is insured by conventional evacuating pumps and the like connected to the envelope 10 at 36a. This pumping system is convenient in some operations but may be dispensed with, when Lenard windows of good life are provided, by sealing olf the tube in the usual manner. In this case, of course, the gasket 36 would be replaced by a permanent glass-to-metal seal.

As shown in exaggerated form by Figure 3, a beam of electrons 37 which passes through the Lenard window formed over opening 11 by the aluminum foil 35 travels substantially directly to the paper strip 12 which is being carried past the Lenard window around roller 17.

It has been determined that the action of the electron beam on the paper record strip is more efficacious when the paper passes as close to the Lenard window as is possible. Hence, it is contemplated by the present invention that the paper strip may be drawn directly over the Lenard window as shown in the fragmentary view of Figure 4. In this figure, there is illustrated a portion of an end cap 34' having a slit-like opening 11' covered by a sheet of aluminum foil 3S. The strip of record paper 12 is drawn past the Lenard window as close thereto as possible. Since the aluminum foil is extremely fragile it has been found desirable to protect the same from the frictional forces of the moving paper strip 12 by disposing a guide member 38 between the aluminum sheet and the paper strip. While this guide member 38', as shown in Figure 4, appears to be of substantial thickness, it is to be borne in mind that the guide 38 should actually be as thin as possible in order to Ikeep the paper strip 12 extremely close to the Lenard window. In the embodiment shown in Figure 4, the guide member 38 performs the additional function of clamping the aluminum sheet 35 onto the top surface of the cap member 34'.

It will be appreciated that, as mentioned briey above, any air molecules between the aluminum foil of the Lenard window and the paper record strip will be ionized by the electron beam traveling toward the paper. This ionization results in some diffusion of the pattern charged electrostatically on the paper by the beam, since the charge, in such case, is the net result of the electrons per se and the ions. This diffusion results in a somewhat objectionable loss of definition in the resultant record and, for this reason, the modification illustrated in Figures 5 and 6 is proposed as another embodiment of the invention.

Figure 5 shows a portion of a cathode ray tube end cap 34 provided with a slit-like opening 11 covered by a very thin sheet of aluminum foil 3S, which latter two reference numerals indicate the Lenard window of this modication.

A rectangular frame 39 is gasketed at 36" to the cap member 34" and is provided with a semi-cylindrical cavity 40 which is adapted to receive a cylindrical paper guide 41. The dimensions of the cylindrical guide 41 are chosen so that the distance between the outer surface of the guide 41 from the surface of the cavity 40 is just suthcient to accommodate the thickness of the paper 12". The width of the cylindrical guide 41 is of such dimension as to permit the guide 41, which has a close t against the corresponding vertical walls 42 of the cavity 40, to t in the cavity, while precluding the entrance of air into the cavity. There are further provided drilled ports 43 leading into the cavity 40, which ports are adapted to be connected to a pump 44 which serves to remove a substantial amount of any air which may have leaked into the cavity through the minute space between the cylindrical guide 41 and the walls of the cavity. By virtue of this vacuum pump 44, the pressure near the Lenard window is reduced to approximately l mm. Hg, thus resulting in fewer air molecules which may be charged by the electron beam in traveling through the space from the Lenard window to the paper.

This reduction in pressure over the outer surface of the Lenard window also reduces the mechanical stresses in the thin aluminum sheet.

In the operation of the apparatus illustrated in Figure l, the strip of record paper 12 which may be in the form of a waxed paper is drawn from supply reel 13, over idler 14, past the Lenard window 11, around idler 17, and thence past the heater 19 to the driving rolls 20-21. According to one mode of operating the apparatus disclosed, the waxed paper 12 may be provided with a uniform electrostatic charge, for example, one of positive polarity, by means of electrodes 15 and 16. As the paper, thus charged, is drawn past the Lenard window, the electron beam 37 as modulated by the signal appearing on control electrode 29 is caused by the deflecting plates 30 to sweep back and forth along the length of the Lenard window slit 11. As explained, the aluminum foil is substantially transparent to the electrons and the beam therefore bombards the paper strip, traveling in a scanning motion transversely of such strip. Assuming that the paper strip has previously been provided with a uniform positive electrostatic charge, the electrons, upon striking the strip, will discharge the same at their points of impact, leaving a pattern for each scanning line, of selectively discharged portions. Assuming the container 23 has been lled with a suitable colored powder which has been given an electrostatic charge of positive polarity, the powder, upon cascading down the scanned strip, will be attracted by the portions of the strip which have been selectively discharged by the electron beam and will be repelled by those positive portions of the strip which have not been so discharged. The excess powder is caught by 5. receptacle 25 and returned to container 23 for reuse. The strip, however, now coated with powder in the areas discharged by the electron beam, is carried past the heater 19 shown, by way of example, as heated by an electric coil 45, where the wax paper is softened. The powder thereby is caused to adhere in a substantially permanent fashion to the softened wax and thus presents a permanent record of the image which had been placed electrostatically on the paper strip by the cathode ray tubes electron beam.

While the example given has indicated the use of a powder provided with a charge of positive polarity, it is also contemplated that the powder may have a negative charge, in which event the resultant record image would be a negative, or reverse, image.

Though wax paper has been described as the recordreceiving material, it has been found that ordinary, uncoated paper will also retain the necessary electrostatic charge, assuming that the atmosphere is not too humid. In the event that a non-waxed paper is used in the practice of this invention, it is to be borne in mind that the powder should be of a thermoplastic composition so that the heater 19 will soften the powder and cause it to adhere permanently to the paper.

In the event that it is not desired to provide the record strip with a uniform positive charge prior to its passing the Lenard window, the invention further contemplates the use of a non-charged paper strip which is selectively charged by the electron beam emanating from the Lenard window. Where apparatus such as that illustrated in Figures 1 through 3 is employed for this mode of operation, it has been found desirable to apply an accelerating voltage to idler roll 17 in order that the electron beam may be caused to travel more quickly toward the paper strip, thus decreasing the diiusion of the beam caused by ionization of air molecules in the space between the window and the paper. Figure 2 indicates by dotted lines a source of accelerating voltage connected to idler roll 17 for the purpose of applying thereto an electrostatic charge opposite in polarity from that of the electron beam.

In the operation of the embodiment shown in Figure the paper 12 travels past the Lenard window spaced but a slight distance therefrom so that there is less likelihood of ionization of air between the aluminum foil 35 and the paper.

Figures 5 and 6, on the other hand, disclose an embod ment which employs a vacuum in the rectangular frame 39. Assuming that the ports 43 are connected to a suitable vacuum pump and that the pressure within the frame is approximately l mm. Hg, the paper 12 will pass around the cylindrical paper guide 41 in front of thc. Lenard window and will be subjected to the action of electron beam 37 substantially without ionization. If the paper 12 had previously been given a uniform electrostatic charge of positive polarity, the electron beam striking the paper would thereby selectively discharge portions of the paper during the scanning operation. The paper would then pass a source of iinely divided colored material which would cascade down the paper and adhere either to the selectively discharged portions of the paper resulting from the electron beams eiect, or to the non discharged portions, depending upon whether the finely divided material possessed a positive or negative charge. The same alternatives as to thermoplastic paper or thermoplastic coating material are available in the operation of this embodiment as in the other embodiments of the invention.

While the invention has been described as employing a powdered material, it is also contemplated that selectively charged or discharged record paper may be contacted by electrostatically charged liquid droplets which would act in a similar manner to that of the powder. Paper has been described as the record strip which receives the electrostatic image but the word paper has been used only by way of example and should not be considered as limiting, since, although paper is the least expensive of materials available, any material capable of holding an electrostatic charge and being selectively discharged may be employed.

Other changes within the scope of the invention as pointed cut in the appended claim will become apparent to those skilled in the art.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

A cathode ray tube recording apparatus comprising a cathode ray tube having an elongated slitlike window in its face, said window being covered by a thin sheet of metallic foil, an elongated sheet of insulating material having a width substantially equal to the length of said window, means for moving said elongated sheet of insulating material past said window at a constant velocity in close proximity to said window, means for intensity modulating an electron beam in said tube, means for causing said electron beam to scan said elongated sheet of insulating material through said window at right angles to the direction of motion of said sheet, whereby a charge pattern is produced on said elongated sheet of insulating material in accordance with the intensity modulation of said beam, means including a substantially airtight enclosure covering said window and the portion of said elongated sheet of insulating material in the immediate vicinity of said window for substantially evacuating the space between said window and said elongated sheet of insulating material, a source of finely divided material, said nely divided material being so charged as to adhere only to the portions of said elongated sheet of insulating material which have received a charge from said electron beam and means for applying said iinely divided material to said elongated sheet of insulating material whereby said finely divided material will adhere selectively to said elongated Sheet of insulating material in accordance with the charge pattern produced thereon by said electron beam and will make a visible pattern on said elongated sheet of insulating material in accordance with the intensity modulation of said beam.

References Cited in the lile of this patent UNITED STATES PATENTS 1,736,456 Matthias Nov. 19, 1929 2,143,214 Selenyi Ian. 10,1939 2,197,050 Kellog Apr. 16,1940 2,200,741 Gray May 14, 1940 2,221,776 Carlson Nov. 19, 1940 2,297,691 Carlson Oct. 6,1942 2,351,889 Strubig June 20, 1944 

